The Natuna Islands chain, which sits between the northwestern tip of Indonesia on the island of Borneo and the southern tip of Vietnam, consists of about 270 islands that form part of Indonesia’s Riau Islands Province with some 70,000 residents.

On Nov. 12, China shocked the countries in the region by issuing a first-ever public statement on the Natuna Islands. According to Hong Lei, China’s Foreign Ministry spokesman, “The Indonesian side has no territorial claim to China’s [Spratly Islands]. The Chinese side has no objection to Indonesia’s sovereignty over the Natuna Islands.”

This is significant because, although the Natuna Islands are outside of China’s self-designated “Nine-Dash-Line” that lays claim to virtually all of the South China Sea, Natuna’s 200-miles exclusive economic zone (EEZ) protrudes into the area defined by the Nine-Dash-Line. To publicly recognize Indonesia’s sovereign right to the Natunas means China’s acknowledgment of Indonesia’s legitimate claim to an EEZ inside China’s self-claimed Nine-Dash-Line.

And this is not something that China has been willing to do, partly because of the inexact nature of the so-called Nine-Dash-Line and partly because China does not want to show weakness to its smaller neighbors who challenge its maritime claims. Beijing’s failure to clarify with Indonesia the competing claims on the Natuna Islands and the EEZ lies at the root of the angst felt by Jakarta for decades.

Traditionally, Indonesian officials have preferred low-key diplomacy with China on the Natuna situation. And China needs Indonesia, too, as the largest and weightiest country in the ASEAN bloc where four members — the Philippines, Vietnam, Malaysia and Brunei — openly dispute China’s maritime claims.

Several past Indonesian leaders have said they received private assurances from China that, since the two countries do not have an island dispute inside the Nine-Dash-Line, China would not dispute Jakarta’s sovereignty over the Natuna Islands. But Beijing has deliberately avoided public discussion of the EEZ issue, which fueled doubts for many in Jakarta over Beijing’s sincerity in those private assurances. Some argued that China was pursuing a Fabian strategy to wear Indonesia down so that the EEZ issue would eventually evaporate.

But Beijing misread Jakarta, because Indonesia seems to have grown increasingly impatient with Beijing’s strategic ambiguity on the EEZ situation.

To make things worse, China began its massive sand-pumping project to reclaim and augment small islands in the Spratly’s chain, further angering not only Vietnam and the Philippines, but also Japan, Australia, the United States and Indonesia. The maritime waters just north of the Natuna Islands have suddenly become the potential flash point of a general war involving the navies of several of the world’s most powerful nations.

The Philippines has been among the most tenacious challengers to China’s ambitions in the South China Sea, having brought Beijing to an international arbitration court in The Hague, where the ruling in favor of Manila is widely expected.

China has been irate over the lawsuit. The official Chinese media has lambasted Manila and the government has emphatically refused to participate in any legal challenge. Last month, however, the Permanent Court of Arbitration in The Hague ruled against Beijing’s attempt to deny the court’s jurisdiction over the matter.

Frustrated by China’s refusal for a clarification and inspired by the Philippine success in The Hague, Jakarta decided to play hardball with Beijing, too.

Under the newly elected President Joko Widodo, Indonesia has stepped up military fortifications on the Natuna Islands. Weeks ago, he ordered more Su-27, Su-30, and F-16 fighter planes and P3-C maritime surveillance and anti-submarine aircraft to the islands, adding more troops to the military base there to demonstrate Indonesia’s resolve to protect its territory and the EEZ areas around the Natunas.

Then, on Nov. 11, Jakarta dropped a bombshell on Beijing. The Indonesian security chief Luhut Panjaitan told reporters that if dialogue with China on the Natuna islands did not yield any result soon, Indonesia might follow the footsteps of the Philippines and bring China to the international arbitration court for a clarification.

The next day, China’s Foreign Ministry spokesman Mr. Hong made history by finally, and openly, announcing China’s willingness to accept Indonesia’s sovereign claim to the Natuna Islands.